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The engine cradle must be lowered on the passenger side to remove the balancer pulley. You will then need to use a flywheel lock to lock the flywheel in place. The cam covers must be removed in order to remove the timing chains to gain access to the pump. As you can see, this is a TON of work and you will only be disappointed when you replace the pump (gear) only to find the problem still exists. The independent mechanic is treating the Northstar engine lilke a small block Chevy engine as based on his analysis that a bad oil pump must be the cause of the low oil pressure. It may be true in a small block Chevy but not so with a Northstar.

Your '96 SLS has the Northstar engine, not the 4.9. Oil pump failures are very rare on those engines. You don't need to remove the oil pan to access the oil pump on a Northstar. The oil pump is behind the timing cover - it is a gerotor style pump and is very durable. Was an aftermarket sensor used when the pressure sensor was replaced? If so, they have been known not to have the same trip point for the low pressure light. You need to temporarily install an oil pressure gage and see what the actual oil pressure is when the low pressure light goes off.

Be sure to lube the o-ring with 525 viscosity refrigerant oil prior to installation.

When you say the gages checked out - I assume the pressures met the requirements in the shop manual for ambient air temp and relative humidity right? If so it is possible the pressure switch is bad. Make sure to change the o-ring that is behind the pressure switch - if you don't, you will have a leak after you swap out the switch.

To add: The low refrigerant code is determined by the high/low side thermistors (temperature sensors), not the pressure switch.

Mr. Eldo, How do you know that you do not have a leak? I would have the system leak checked prior to throwing parts at it. The pressure sensor rarely causes a problem. Sometimes the high side or low side thermisters will go bad but those failures are rare (unless someone installs the orifice tube in the wrong direction - that will destroy the low side thermister.). Check the compressor body for oily/greasy residue - that may indicate the compressor case o-rings are leaking.

I would need to double check the service manual but I think the pressure switches have schrader valves in the lines so the refrigerant would not need to be recovered. The high and low side temp. sensors do not and the refrigerant must be recovered prior to replacement. Out of curiousity, why to you think the pressure switch needs to be replaced?

I have read testimony from people who've added Freeze-12 to R-12 with no issues (I don't believe everything I read on the internet). Couldn't I just tell the AC mechanic that the system was contaminated? Besides that, I don't plan to repair it if it breaks, and I won't be selling this car. This is a one time all or nothing- fix it or bypass it situation, and I want to get it done as cheaply as possible. Knowing that I don't plan to pay hundreds of dollars to solve this issue, how would I drain the R-12 from the system? Am I better off buying some R12 off ebay? Do you have a better suggestion? thanks for the advice Just because someone on the internet has performed an improper repair and got the system to function does not mean that it will hold up long term or the two refrigerants won't react and create an acid that will eat the evaporator core... You can't legally vent ANY refrigerant to the atmosphere. If it were my car, I would have the leak located and repaired. It could be that it is so small of a leak that it took years to leak down enough for the low refrigerant code to set. Then have a shop recharge it with R-12. If you just want to top it off you could buy a can of R-12 on ebay but you'll need a charging hose also. You also need EPA-609 certification to buy R-12 even off ebay although there are some sellers who don't ask for an EPA number. Improper repair techniques and venting of refrigerants is why R-12 is restricted and costs so much these days...

Ok great information, thanks. I've gathered that a kit with special fittings and hoses is required to add Freeze-12 to an R12 system. Add that to the fact that Freeze-12 appears to contain R-134a which can wear out seals on an R-12 system, and it sounds like a bad solution. Thanks for the advice! Edit: After researching all morning I think I've made up my mind to try Freeze-12. I can't find any reviews on Autofrost, and I can't find anyone who supplies it. I have seen a dozen or so good reviews for Freeze-12, and it is very cheap. If it wears the seals out or leaks then I will bypass it. I will be using the kit below, and plan to just add the Freeze-12 to whatever R-12 remains in the system. I will have to double check, but I think mine holds 4.5lbs. I'll add the oil charge initially then the leak stop later if the system gets low again. Any tips or pointers? http://cgi.ebay.com/ebaymotors/FREEZE-12-R...0262303006& Please do not add Freeze 12 to the existing R-12 charge... first, it is illegal, second, the R-134a can react with the R-12 and eat the system from the inside out, and third, it may contaminate someone's recovery machine in the event the car is serviced by an AC shop. Your system capacity is in the 2.0 lb. range. Leak-stop for AC systems is snake oil.... None of it works long term and if the system needs to be recovered for proper service, some of the stop leaks contaminate the filter on a recovery machine. If you do not find and repair the leak, the R-134a, Freeze-12, etc. will leak out FASTER than the R-12 due to the smaller molecule size.

If you never intend to use the A/C, just leave it - the compressor won't sieze. The ACM disables the compressor when the refrigerant gets too low to prevent it from being damaged. It would be interesting to know where the system is leaking. If you intend to use an alternative refrigerant which would be a blend, it is critical that you repair any leaks as any leaks will compromise the blend ratio of the alternative refrigerant. Look for oily/greasy residue on the A/C components (lines, fittings, pressure switches, compressor body, compressor clutch, etc.). It could be a simple shaft seal on the compressor. Freeze-12 is a blend of R-134a and R-142b - the R-142b is in the mix to blend and circulate the mineral refrigerant oil in the system. I have not used it but have used Autofrost R-406a in my old Park Avenue with excellent results. The caution is the Cadillac systems use thermisters to sense the proper refrigerant quantity - a lesser amount of the blend refrigerants are required for optimum performance and a lesser amount of refrigerant in the system may set the low refrigerant codes/message and disable the compressor.

Why do you want to bypass the compressor? Is the clutch bearing bad?

I tow a covered, two-place snowmobile trailer with my STS but that's about the limit that I'd tow before I'd change tow vehicles. There is a lot of wind resistance fron the cover that adds to the effective weight of the trailer. My Fleetwood Brougham is rated to tow 7000 lbs. but I store that car for the winter... The STS has PLENTY of power to pass on a two lane road with the snowmobile trailer in tow.

I doubt it's as simple as a stuck waterpump tensioner or plugged line to the surge tank but it would be unbelievable it it was. I've never used a kit like that before - I may try it if the spark plug air adapter is inconclusive. I have one just about finished on my bench. The troubleshooting will commence Friday evening....Stay tuned.

I will take plenty of photos. In the back of my mind, I am hoping it is a plugged return line to the surge tank or a frozen waterpump belt tensioner....

Timeserts are the only thread repair products that will successfully repair Northstar headbolt holes. I will be doing that job on my '97 STS in a couple of weeks.

Sorry to hear that Kevin. My knee-jerk would be to suspect the resistor connections. Yeah - I need to solder it in place and see what happens. I now have another project on my hands as you know. The Fleetwood comes out of winter storage in two weeks - about the time I want to start timeserting the STS.....

Just to make one point clear for anyone willing to go with non-electronic struts / shocks. The resistor value that fooled the CVRSS OBD on my '98 was a 4.7k Ohm, 1/2 Watt. That is 4,700 Ohms, 1/2 Watt. The Radio Shack package will say "4.7k-Ohm" and is #271-1124. For a '97 and earlier (with RSS), if the 4.7k Ohm does not work (which I doubt), I would try a 10k Ohm, 1/2 Watt resistor. That is 10,000 Ohms. Radio Shack #271-1126. Feedback is always welcome. Jim, I've had the "SERVICE RIDE CONTROL" message on my '96 for quite awhile. The cause is the right rear shock - the damper is shorted - I think the code was RS0028. I tried the 10K resistor yesterday afternoon and is has supressed the message. I took the car on a 1-1/2 mile test run and there was no message. Ususlly, the message pops up before I reach the end of the driveway. I asked my wife afout the service ride control message last night - she said it still comes up but not at every ignition cycle.

Glad to be able to make a contribution to the cause. I was motivated by the fact that my factory installed stuts are overdue for replacement (145,xxx miles) and I am still changing my mind every day on the OEM versus passive decision. Clearing the nuisance message would quickly become a pain for me. Reading here and on cadillacforums.com convinced me that the aftermarket passive strut suppliers where taking the wrong approach to defeating the message with a low resistance value, high wattage, resistor. I just had to know how to properly and efficiently defeat the message just in case I decide to go with passive on the front of my '98. Yeah - clearing the message is sort of a PITA - in my case, my wife is the principle driver of the SLS but every time I drive the car, I was annoyed at the message. I too wonder why the aftermarket suppliers continue to sell resistors that don't work....

Just to make one point clear for anyone willing to go with non-electronic struts / shocks. The resistor value that fooled the CVRSS OBD on my '98 was a 4.7k Ohm, 1/2 Watt. That is 4,700 Ohms, 1/2 Watt. The Radio Shack package will say "4.7k-Ohm" and is #271-1124. For a '97 and earlier (with RSS), if the 4.7k Ohm does not work (which I doubt), I would try a 10k Ohm, 1/2 Watt resistor. That is 10,000 Ohms. Radio Shack #271-1126. Feedback is always welcome. Jim, I've had the "SERVICE RIDE CONTROL" message on my '96 for quite awhile. The cause is the right rear shock - the damper is shorted - I think the code was RS0028. I tried the 10K resistor yesterday afternoon and is has supressed the message. I took the car on a 1-1/2 mile test run and there was no message. Ususlly, the message pops up before I reach the end of the driveway. Good deal! Now we know for sure that the RSS and CVRSS system message can be easily and inexpensively turned off with the appropriate value resistor. Now we need someone with the magnetic fluid struts to do the same test. I suspect the 10K resistor would defeat the message on that ride control module as well. How do you plan to water proof and insulate the installation Kevin? Well, Right now, I just inserted the leads of the resistor into the body harness connector and taped the whole thing with electrical tape. If long term testing prooves successful, I'll probably cut the wires on the shock side, solder the resistor in place and use heat shrink tubing and RTV to weatherproof the connection. When I need to replace the rear shocks, I'll probably go with the AC Delco passive air leveling shocks unless I get a deal on electronic shocks. The actuator in the original shock on the right rear bought the farm at 72,000 miles. Thanks for the information on the resistor values. I was going to experiment with values but that project didn't make high enough priority on my list...

It was Jim's idea for the resistor value - I just tried it out and it worked. I'll know more after I have some more miles on it.

Just to make one point clear for anyone willing to go with non-electronic struts / shocks. The resistor value that fooled the CVRSS OBD on my '98 was a 4.7k Ohm, 1/2 Watt. That is 4,700 Ohms, 1/2 Watt. The Radio Shack package will say "4.7k-Ohm" and is #271-1124. For a '97 and earlier (with RSS), if the 4.7k Ohm does not work (which I doubt), I would try a 10k Ohm, 1/2 Watt resistor. That is 10,000 Ohms. Radio Shack #271-1126. Feedback is always welcome. Jim, I've had the "SERVICE RIDE CONTROL" message on my '96 for quite awhile. The cause is the right rear shock - the damper is shorted - I think the code was RS0028. I tried the 10K resistor yesterday afternoon and is has supressed the message. I took the car on a 1-1/2 mile test run and there was no message. Ususlly, the message pops up before I reach the end of the driveway.

It is not a design flaw - there are millions of Northstar engines out there that do not have any issues with the head gaskets. You have been lucky enough to find three that do have issues though. Hopefully, I won't jinx myself but my '96 does not have any head gasket issues. Helicoils will NOT work - they are not strong enough and will pull right out when the head bolts are torqued. The head bolts are torque to yield bolts so they do strech a bit during installation but that assures a constant clamping force. When a head bolt lets go, it is the threads in the block that are the cause.

Congratulations on using such a fine grit paper. THAT was important. And I suspect you know it. Many folk think they can just file or sand ANY contacts to bring them back to life. And, of course, they do revive . . . . for a week or two. What people often don't realize is that by filing contacts they have enormously increased the surface-to-air ratio of the contacts. Perhaps hundreds fold or more. This promotes rapid oxidation, i.e. rust. That's shortly followed by even worse contact resistance. The best solution is to use a "burnishing" tool or apply that contact cleaner to a strip of paper or very thin leather and draw it repeatedly back and forth between the closed contacts. You'll wind up with clean contacts without developing the extra surface area that promotes rust and even worse problems than you started with. Regards, Warren Good point on the contact cleaner and a piece of paper. When cleaning points on a point type ignition on a snowmobile, it would do the same thing if you filed the points. Piece of paper and some contact or brake cleaner does the trick. Spence Spence, Out of curiousity, how old of snowmobile do you have that has ignition points???

You must put the ECM into "Set Timing Mode" by jumping the A&B terminals on the ALDL connector. Then use a timing light pointed at the balancer to verify the timing as you rotate the distributor. The angle in the balancer does not correlate to rotation of the distributor.

There is an o-ring that is on the pump cartridge and a silicone "o-ring" seal that fits in a groove in the cover that seats against the housing.